Book Review

Contaminant fingerprints in fat tell all

Anyone who has attempted a diet (I think that covers pretty much…everyone over the age of 25) understands that body fat can be difficult to get rid of. Body fat can store organic contaminants that are ingested or absorbed, leaving a record of chemical exposure within the fat deposits. Researchers in Brazil recently put this storage tendency to the test. They analyzed fat from stranded dolphins using a new technique to get a wide-angle view of all organic contaminants stored within blubber from four dolphins. Organic contaminants or POPs are human-created compounds that tend to stick around in the environment and can cause problems for flora and fauna alike.

Bottlenose dolphins are a great organism for studying organic contaminants because they display high site fidelity. High site fidelity means that the dolphins generally hang around the coast in one region, so POPs identified from dolphin tissue pretty much represent the POPs freely available in the surrounding region’s air, water, and food web.

Bottlenose dolphins (Tursiops truncatus) are a common sight around shores worldwide; they like to hang out in the same coastal regions over the course of their life (Caroline Weir).

How to get fat to fess up: a chemist’s strategy

Researchers took fat samples from stranded dolphins, cleaned them up to isolate the POPs from the fatty tissue, and then injected the cleaned up samples into a GCxGC/TOF-MS instrument (aka machine, not a cousin of the violin or anything). Don’t let the acronym scare you away; you’d say this out loud as, “Gas chromatography coupled with time of flight mass spectrometry”. Gas chromatography (GC) is a chemist’s way of separating different compounds in a sample by size. This particular technique used two different separations, where the sample was first separated by the primary GC, and then the separated sample was transferred to another GC unit, or column, and immediately separated again using a second GC. The result was a sample where unique compounds were well separated from one another as they travel through the instrument to the detector.

Using two GC units helps researchers achieve a better separation of compounds, allowing the resulting signals to be read as unique and discrete compounds like in the top panel. (chemwiki.ucdavis.edu)

A special detector called a TOF-MS was then used to detect what is actually in the sample. The TOF-MS “reads” what’s in the sample using the time it takes each compound to reach the detector to produce a clear picture of all the chemicals within a sample to be read/interpreted by the analyst. This is different from other forms of GC/MS that may only look for a handful of specific compounds at a time.

The GCxGC/TOF-MS system is represented by this diagram; although the system may have lots of fancy parts, notice that the gas chromatography part of the system on the right has two columns, facilitating the great separation important for this technique. After being separated, the sample is transferred to the detector on the left where it is energized and its travel time measured to produce an interpretable signal (biotech.wisc.edu)

With this special and powerful technique, researchers were able to see a slew of compounds in dolphin fat that they had no idea were there, similar to results seen in this previous oceanbites article. They found 158 different compounds from 32 different families in the fat from the four dolphins; notably, almost 90% of the compounds found in the Brazilian dolphin fat are not regularly looked for in regular POP monitoring efforts. This result is really similar to what GCxGC/TOF-MS found when looking at fat from Southern California dolphins. This is important because this means that environmental monitoring activities around the globe that are supposed to keep tabs on possibly dangerous chemicals in the environment may be missing the bulk of contaminants by only looking for a few specific compounds.

Well, what was actually found?

42% of the identified compounds were from human sources, 16% were from natural sources, 2.5% were from both human and natural sources, and 39% were unknown. DDT-related compounds were the most abundant group of POPs found; DDT was used as a pesticide until recently in Brazil, likely explaining the high levels of this particular compound and its related breakdown cousins. Interestingly, a type of natural chemical was the second most abundant compound type in the dolphin tissue.

Most of the compounds found with this special technique are not normally looked for in regular POP monitoring (Alonso et al. 2017)

A natural chemical? Must be good for ya!

Ehhhhh, not quite. Recent research has found that phytoplankton, algae, and invertebrates create chemicals for defense or when they are stressed; these chemicals or naturalproducts can still be dangerous to surrounding creatures. The ones found in dolphin tissue as the second most abundant group, called MeO-BDEs or methoxylated brominated diphenyl ethers, have been found elsewhere to have related toxic effects and transformations. This is a problem, considering that other recent research from the San Francisco Bay has found that these natural products may be increasing in the environment due to human impacts in marine and coastal environments.

So what does all this chemical doom and gloom mean?

Although the paper may be a tad overwhelming in its finding of dozens and dozens of chemicals in dolphin fat, the situation isn’t completely dire. The research suggests the need for improved monitoring programs, so that a greater range of POPs are monitored in air, water, and living things to reflect the large number of chemicals that are realistically in the environment (and in us!). As well, the findings of the paper also suggest the need to keep natural products in mind; these compounds are highly abundant, may be increasing in the environment, but aren’t necessarily good for people or creatures.

I am a third year PhD student at the University of Rhode Island Graduate School of Oceanography in the Lohmann Lab. My current research interests include environmental chemistry, water quality, as well as coastal and seabird ecology. When not in the lab, I enjoy diving, surfing, and hanging out with my dog Gypsy.